ModelStandaloneSetup.doSetup();
CommonStandaloneSetup.doSetup();
Injector INJECTOR = new CommonStandaloneSetup().createInjectorAndDoEMFRegistration();
ResourceSet rs = INJECTOR.getInstance(XtextResourceSet.class);
URI uri = URI.createFileURI("path to dsl file");
Resource resource = rs.getResource(uri, true);
FormatterRequest formatterRequest = new FormatterRequest();
formatterRequest.setEnableDebugTracing(true);
((MapBasedPreferenceValues) formatterRequest.getPreferences()).put("indentation", "    ");
TextRegionAccessBuilder textRegionAccessBuilder = new TextRegionAccessBuilder();
ITextRegionAccess access = textRegionAccessBuilder.forNodeModel((XtextResource) resource).create();
formatterRequest.setTextRegionAccess(access);
List<ITextReplacement> replacements = formatter.format(formatterRequest);
String formatted = formatterRequest.getTextRegionAccess().getRewriter().renderToString(replacements);